Semiconductor device and a method of manufacturing the same

ABSTRACT

A semiconductor device having redistribution interconnects in the WPP technology and improved reliability, wherein the redistribution interconnects have first patterns and second patterns which are electrically separated from each other within the plane of the semiconductor substrate, the first patterns electrically coupled to the multi-layer interconnects and the floating second patterns are coexistent within the plane of the semiconductor substrate, and the occupation ratio of the total of the first patterns and the second patterns within the plane of the semiconductor substrate, that is, the occupation ratio of the redistribution interconnects is 35 to 60%.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/352,591filed Jan. 12, 2009 now U.S. Pat. No. 7,812,456. Also, the disclosure ofJapanese Patent Application No. 2008-33012 filed on Feb. 14, 2008including the specification, drawings and abstract is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method ofmanufacturing the same, in particular, to an effective technologyapplied to a semiconductor device having redistribution interconnects ina WPP (Wafer Process Package) technology.

The WPP technology (or WLP (Wafer Level Package) technology) is atechnology of integrating a wafer process (pre-process) and a packageprocess (post-process) and finishing packaging while in the waferprocess. This WPP technology is advantageous because it needs far fewersteps than a technology in which the package process is performed foreach of semiconductor chips cut out from a semiconductor wafer. In thepackage process of the WPP technology, redistribution interconnectselectrically coupled to semiconductor elements formed in the pre-processare formed by the plating process and covered with a surface protectivefilm.

Japanese Unexamined Patent Publication No. 9 (1997)-306914 (patentdocument 1) discloses a technology for forming dummy plating patternsover a semiconductor wafer together with real patterns which become theactual interconnects as a method of forming interconnects forsemiconductor elements. This patent document 1 is aimed to form uniformplating interconnects stably as interconnects for semiconductor elementsand does not teach the stable formation of redistribution interconnectsin the WPP technology.

[Patent document 1]

Japanese Unexamined Patent Publication No. 9 (1997)-306914

SUMMARY OF THE INVENTION

In high-speed SRAM (Static Random Access Memory) and CMOS (complementaryMetal Oxide Semiconductor) logic products, for example, theabove-described WPP technology is employed for the purpose of areduction in package cost and speedup and they have a package structureso as to permit flip chip coupling to a package substrate via bumpelectrodes made of solder.

When WPP is adopted, a semiconductor device is manufactured by thefollowing steps. First, semiconductor elements such as MISFET (MetalInsulator Semiconductor Field Effect Transistor) are formed over themain surface of a semiconductor wafer, followed by the formation of aplurality of multi-layer interconnects over the semiconductor elements.Then, a silicon nitride film and a silicon oxide film are formed overthe multi-layer interconnects and further a polyimide resin film isformed over the silicon oxide film. The steps up till now are the waferprocess of the WPP technology and the subsequent steps are the packageprocess of the WPP technology.

Subsequently, the silicon oxide film, the silicon nitride film and thepolyimide resin film are patterned to form an opening portion having abottom surface from which the uppermost-level interconnect is exposed. Athin electrode layer (barrier layer/seed layer) is formed over thepolyimide resin film including the inside of the opening portion, andredistribution interconnects are formed over the electrode layer byusing the plating process. The redistribution interconnects are eachmade of, for example, a film stack of a copper film and a nickel film.After the formation of a polyimide resin film over the redistributioninterconnects, patterning is carried out to expose end portions of theredistribution interconnects. Bump electrodes are then formed over theexposed end portions of the redistribution interconnects. In such amanner, packaging is performed in the form of a semiconductor wafer,thereby making it possible to manufacture a semiconductor device havingredistribution interconnects and bump electrodes coupled to theredistribution interconnects.

The inventors of the present invention have found that the semiconductordevice using this WPP technology have problems that appearanceabnormalities (large grain diameter and surface roughness) occur in theredistribution interconnects formed by using the plating process andthat there is a difference in film thickness between the center portionand the peripheral portion of the semiconductor wafer. Particularly, inthe center portion of the semiconductor wafer, the film thickness ofeach redistribution interconnect is small and appearance abnormalitiesare marked. The bump electrode formed over one end portion of theredistribution interconnect having appearance abnormalities reduces thereliability of the semiconductor device by peeling. Therefore, theproduction yield of the semiconductor device is reduced by judging theappearance abnormalities of the redistribution interconnects asfailures.

According to studies conducted by the inventors of the presentinvention, the appearance abnormalities of the redistributioninterconnects have dependence upon redistribution interconnect patternsand concentrate at the end portions of the redistribution interconnectsnear the boundary between a region A where the redistributioninterconnects electrically coupled to semiconductor elements are formedand a region B where the redistribution interconnects are not formed.That is, it is considered that an electric field is apt to concentrateat the end portions of the redistribution interconnects near theboundary from the viewpoint of the plating process, thereby causing thelocal growth of the current density to increase the crystal grain sizeof the redistribution interconnects. Therefore, to cope with theappearance abnormalities of the redistribution interconnects, it isconceivable that the redistribution interconnects should also be formedin the region B where the redistribution interconnects are not formed.However, the appearance abnormalities may occur at the end portions ofthe redistribution interconnects due to a difference in the density ofthe redistribution interconnects only when the redistributioninterconnects are formed in the region B. Then, even in the local regionsuch as the above region A, it is necessary to prevent a largedifference in the density of the redistribution interconnects.

The cause of producing the difference in the thickness of theredistribution interconnect between the center portion and theperipheral portion of the semiconductor wafer is considered to be that aplating current for obtaining an appropriate film thickness cannot besecured because the plating current value at the time of forming theredistribution interconnects depends upon the occupation ratio of theredistribution interconnects within the plane of the semiconductorwafer. Therefore, the difference in the thickness of the plating film(film thickness of the redistribution interconnect) must be reduced bythe occupation ratio of the redistribution interconnects in the in-planeregion of the semiconductor wafer.

It is an object of the present invention to provide a technology forimproving the reliability of a semiconductor device.

The above and other objects and new feature of the present inventionwill become apparent from the description of this text and theaccompanying drawings.

A brief description is subsequently given of a typical one of theinventions disclosed in this application.

According to an embodiment of the present invention, redistributioninterconnects in the WPP technology have real patterns (first patterns)and dummy patterns (second patterns) which are electrically separatedfrom each other within the plane of a semiconductor substrate. The realpatterns electrically coupled to a plurality of multi-layerinterconnects and floating dummy patterns are formed within the plane ofthe semiconductor substrate.

A brief description is given of an effect obtained by a typical one ofthe inventions disclosed in this application.

According to an embodiment, since the difference in the density of theredistribution interconnects formed within the plane of thesemiconductor substrate can be reduced, the reliability of thesemiconductor device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor device according to anembodiment of the present invention;

FIG. 2 is an enlarged plan view of the semiconductor device shown inFIG. 1;

FIG. 3 is a sectional view of the key section of the semiconductordevice shown in FIG. 1;

FIG. 4 is an enlarged plan view of a semiconductor device studied by theinventors of the present invention corresponding to FIG. 2;

FIG. 5 is a flow chart of the manufacturing process of the semiconductordevice according to the above embodiment of the present invention;

FIG. 6 is a diagram showing processing patterns in the design step ofFIG. 5;

FIG. 7 is a diagram showing processing patterns in the design step afterFIG. 6;

FIG. 8 is a diagram showing processing patterns in the design step afterFIG. 7;

FIG. 9 is a diagram showing processing patterns in the design step afterFIG. 8;

FIG. 10 is a diagram showing processing patterns in the design stepafter FIG. 9;

FIG. 11 is a plan view of the semiconductor device in the wafer step andthe package step shown in FIG. 5;

FIG. 12 is a sectional view of the semiconductor device after FIG. 11;

FIG. 13 is a sectional view of the semiconductor device after FIG. 12;

FIG. 14 is a sectional view of the semiconductor device after FIG. 13;

FIG. 15 is a sectional view of the semiconductor device after FIG. 14;

FIG. 16 is a sectional view of the semiconductor device after FIG. 15;

FIG. 17 is a sectional view of the semiconductor device after FIG. 16;

FIG. 18 is a sectional view of the semiconductor device after FIG. 7;

FIG. 19 is a diagram showing the relationship between the platingcurrent and the occupation ratio of redistribution interconnects;

FIG. 20 is a diagram showing the relationship between the thickness of asemiconductor wafer and the warpage of the semiconductor wafer;

FIG. 21 is a plan view of a semiconductor device according to anotherembodiment of the present invention; and

FIG. 22 is a sectional view of the key section of the semiconductordevice shown in FIG. 21.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detailhereinunder with reference to the accompanying drawings. In all thedrawings for explaining the embodiments, members having the samefunctions are given the same reference symbols and their repeateddescriptions may be omitted. In the drawings for explaining thefollowing embodiments, even when they are plan views for making theconfiguration of the present invention comprehensive, they may behatched.

Embodiment 1

The semiconductor wafer of this embodiment is a semiconductor devicehaving a CSP (Chip Size Package) structure and the WPP technology isused to manufacture the same. CSP is a generic term for packages whichare the same or larger in size than a semiconductor chip. Since they canbe reduced in size and weight and the length of an internal interconnectcan be reduced, a signal delay and noise can be suppressed. Thecharacteristic structure of the semiconductor device according to thisembodiment will be described with reference to FIGS. 1 to 3.

FIG. 1 is a plan view of a semiconductor chip 1C in this embodiment andan enlarged part (region A surrounded by the broken line) thereof. FIG.2 is a more enlarged plan view of the semiconductor chip 1C shown inFIG. 1. Real patterns 2 and dummy patterns 3 shown in FIG. 2 areredistribution interconnects in the WPP technology. To make explanationeasy, the dummy patterns 3 are not shown in FIG. 1. The real patterns 2are electrically coupled to internal circuits including thesemiconductor elements of the semiconductor chip 1C, and the dummypatterns 3 are electrically separated, that is, floated. FIG. 3 is asectional view of the key part of the semiconductor chip 1C.

As shown in FIG. 1, the rectangular semiconductor chip 1C has a centralregion 80 (region surrounded by the one-dot broken line) and aperipheral region 90 around the central region 80 within the plane. Thesurface of the semiconductor chip 1C is covered with a surfaceprotective film which is, for example, a polyimide resin film, and bumpelectrodes (not shown) for communicating a signal between the outsideand the inside of the semiconductor chip 1C are formed in openingportions formed in the surface protective film. The bump electrodes areformed over the land electrodes 2 a of the real patterns 2 in theenlarged region A of the semiconductor chip 1C in FIG. 1. Even in thesemiconductor chip 1C which is a small-sized semiconductor device havinga CSP structure, regions (the area of the land electrode 2 a) in whichthe bump electrode is formed can be secured by leading the real patterns2 (redistribution interconnects) toward the central region 80 from theperiphery of the semiconductor chip 1C. The real patterns 2 are formedin the peripheral region 90.

As shown in FIG. 2, within the plane of the semiconductor chip 1C, thereal patterns 2 and the dummy patterns 3 are coexistent. They are formedat the same time as redistribution interconnects in the WPP technologyand electrically separated from each other (see FIG. 3). As describedabove, the real patterns 2 are formed in the peripheral region 90 andthe dummy patterns 3 are formed in the central region 80 and theperipheral region 90 located between real patterns 2. By forming thedummy patterns 3 in the central region 80 and the peripheral region 90,the redistribution interconnects are distributed almost uniformly withinthe plane of the semiconductor chip 1C and the difference in the densityof the redistribution interconnects can be reduced more than when thereare no dummy patterns 3.

The circular land electrode 2 a located at one end of each of the realpatterns 2 has a diameter of, for example, 108 μm and a pitch of, forexample, 180 μm. The circular dummy pattern 3 has a diameter of, forexample, 34 μm and a pitch of, for example, 50 μm. The planar shape ofthe dummy pattern 3 may be polygonal with all the corner portions havinga blunt angle to ease stress.

The processing size of the dummy pattern 3 is smaller than theprocessing size of the real pattern 2. Thereby, the dummy pattern 3 canbe formed between real patterns 2 in the peripheral region 90, and theredistribution interconnects can be distributed almost uniformly withinthe plane of the semiconductor chip 1C. The size of the dummy pattern 3is larger than the minimum line width of the redistribution interconnectand such that it is not lost in the step of removing a barrier layer anda seed layer after the formation of the redistribution interconnects.

As shown in FIG. 3, multi-layer interconnects including a third-layerinterconnect 39, a fourth-layer interconnect 40 and a fifth-layerinterconnect 44 are formed over a semiconductor substrate 1S configuringthe semiconductor chip 1C. The multi-layer interconnects serve to form acircuit by electrically coupling a plurality of semiconductor elementsformed below the multi-layer interconnects. A thin silicon oxide film 45and a thin silicon nitride film 46 are formed as passivation films overthe semiconductor substrate 1S to cover the multi-layer interconnects.The silicon oxide film 45 and the silicon nitride film 46 are bothinorganic insulating films and can be formed by plasma CVD.

A polyimide resin film 49 which is an organic insulating film is formedover the silicon nitride film 46. Redistribution interconnects 57 whichare each made of a film stack of a copper film 55 and a nickel film 56formed by the plating process are formed over the polyimide resin film49. The redistribution interconnects 57 configure the real patterns 2and the dummy patterns 3 as shown in FIG. 1 and FIG. 2. A polyimideresin film 58 which is an organic insulating film is formed over thepolyimide resin film 49 as a surface protective film (insulating film)to cover the redistribution interconnects 57.

The reason why the surface protective film is an organic insulating filmmade of a polyimide resin or the like is that the handling of thesemiconductor chip is made easy by forming a relatively soft organicinsulating film as the uppermost layer because the insulating film isapt to be cracked at the time of handling (carrying) the semiconductorchip and it is difficult to handle it when the uppermost insulating filmis an inorganic insulating film.

An opening portion 59 is formed in the polyimide resin film 58 partiallyoverlying the redistribution interconnect 57 of the real pattern 2, andpart of the redistribution interconnect 57 of the real pattern 2 isexposed to configure the land electrode 2 a. This land electrode 2 aserves as an external electrode for the semiconductor chip 1C. Further,a bump electrode 60 is formed over the land electrode 2 a in such amanner that it is electrically coupled to the land electrode 2 a tocommunicate a signal with the outside and carry out coupling with theoutside by mounting. A signal can be communicated with the outside bycoupling a wire bonding to the top of the land electrode 2 a withoutforming the bump electrode 60.

The redistribution interconnects 57 are formed to complete the packagingof a semiconductor wafer and have the function of coupling thefifth-layer interconnect 44 which is the uppermost-level interconnect ofthe multi-layer interconnects to the bump electrode 60. That is, theredistribution interconnects 57 serve as a leading interconnect forcoupling the fifth-layer interconnect 44 to the bump electrode 60. Inother words, it can be said that the redistribution interconnects 57serve as an interposer for changing the spacing of the fifth-layerinterconnects 44 to the spacing of the bump electrodes 60.

The redistribution interconnect 57 of the real pattern 2 overlies partof the fifth-layer interconnect 44 which is the uppermost-levelinterconnect of the multi-layer interconnects and is electricallycoupled to the multi-layer interconnects including the fifth-layerinterconnect 44 in the opening portion 50 formed in the silicon oxidefilm 45, the silicon nitride film 46 and the polyimide resin film 49 tocommunicate a signal with the outside.

Meanwhile, the redistribution interconnect 57 of the dummy pattern 3 iscovered with the polyimide resin film 49 and the polyimide resin film 58which are organic insulating films, electrically separated from themulti-layer interconnects and the real pattern 2 and floating.Therefore, the dummy pattern 3 does not communicate a signal with theoutside. However, the difference in the density of the redistributioninterconnects formed by the plating process is reduced by forming thedummy patterns 3, thereby making it possible to prevent the occurrenceof appearance abnormalities in the real patterns 2. Further, sinceabnormalities failure such as the peeling of the bump electrode 60formed over the real pattern 2 free from appearance abnormalities can beprevented, the reliability of the semiconductor device can be improved.

A description is given of a case where the dummy patterns 3 are notformed with reference to FIG. 4. FIG. 4 is an enlarged plan view of asemiconductor chip 1C′ corresponding to the semiconductor chip shown inFIG. 2 and studied by the inventors of the present invention. The otherconfiguration is the same as that of the semiconductor chip 1C shown inFIGS. 1 to 3.

As shown in FIG. 4, 2 g of copper (copper film 55) or nickel (nickelfilm 56) grains formed by the plating process becomes large at the endportions (land electrodes 2 a) of the real patterns 2 in the peripheralregion 90 where the real patterns 2 are formed and near the boundarybetween the central region 80 and the peripheral region 90 when thedummy patterns are not formed in the central region 80 where the realpatterns 2 are not formed to roughen the surface, thereby causingappearance abnormalities. Further, it is understood that appearanceabnormalities occur in the real patterns 2 between the real patterns 2on the inner side of the peripheral region 90. The appearanceabnormalities can be confirmed by a microscope.

However, in this embodiment, the occurrence of appearance abnormalitiesin the real patterns 2 can be prevented as shown in FIG. 2 by thecoexistence of the dummy patterns 3 and the real patterns 2. Stated morespecifically, the occurrence of appearance abnormalities in the realpatterns 2 can be prevented by forming the redistribution interconnects57 as the dummy patterns 3 in the central region 80 excluding theperipheral region 90 where the real patterns 2 of the redistributioninterconnects 57 are formed. Further, the occurrence of appearanceabnormalities in the real patterns 2 can be prevented more by formingthe redistribution interconnects 57 of the dummy patterns 3 between thereal patterns 2 in the peripheral region 90 where the real patterns 2 ofthe redistribution interconnects 57 are formed. This is considered to bebecause the difference in the density of the redistributioninterconnects 57 comprised of the real patterns 2 and the dummy patterns3 formed by the plating process in local regions such as the regionsbetween the real patterns 2.

In this embodiment, the redistribution interconnects 57 in the packageprocess of the WPP technology are formed over the polyimide resin film49 which is an organic insulating film and the polyimide resin film 58which is an organic insulating film is formed as a surface protectivefilm to cover the redistribution interconnects 57. Although the dummypatterns 3 are thereby floated (electrically separated), adhesionbetween the polyimide resin film 49 and the polyimide resin film 58 canbe ensured because the same type of organic simulating films are used.

The expansion and contraction of the redistribution interconnects 57 andthe polyimide resin films 49 and 58 surrounding the redistributioninterconnects 57 occur in a reliability test in which temperaturecycling between a low-temperature and high-temperature is repeated.However, the generated stress can be eased by processing the dummypatterns 3 to a smaller size than the processing size of the realpatterns 2.

A description is subsequently given of a method of manufacturing thesemiconductor device in this embodiment with reference to FIGS. 5 to 20.FIG. 5 is a flow chart of the manufacturing process of the semiconductordevice in this embodiment, FIGS. 6 to 10 show processing patterns in thedesign step, and FIGS. 11 to 18 are a plan view and sectional views ofthe semiconductor device in the wafer step and the package step.

As shown in FIG. 5, briefing the manufacturing process of thesemiconductor device in this embodiment, the layout of semiconductorelements and circuit wirings are first designed in the design step(S100). Then, in the wafer step (S200), so-called “pre-process” in themanufacture of the semiconductor device is carried out to formsemiconductor elements. Then, in the package step (S300), so-called“post-process” in the manufacture of the semiconductor device is carriedout to form redistribution interconnects as lead lines and package them.In the WPP technology, this wafer step and the package step are carriedout on a semiconductor wafer.

A description is specifically given of the pattern design of theredistribution interconnects 57 in the design step (S100). The design ofthe other configuration may be carried out by a known method using acomputer in consideration of DFM (design for manufacturing).

As shown in FIG. 6, dummy processing patterns 3 p having a predetermineddiameter x1 and a predetermined pitch x2 are formed in a predeterminedregion P of a semiconductor wafer (semiconductor chip) by using acomputer (S110). The dummy processing patterns 3 p have a 64 angledplanar shape, a diameter x1 of 34 μm and a pitch x2 of 50 μm anduniformly arranged in the region P. Unrequired dummy processing patterns3 p are removed until the final design stage. The dummy patterns 3 ofthe above-described redistribution interconnects 57 are designed to belarger than the minimum line width and the minimum spacing of theredistribution interconnects 57 and smaller than the land electrodes 2 aof the real patterns 2 of the redistribution interconnects by theremaining dummy processing patterns 3 p which are not removed.

Subsequently, as shown in FIG. 7, real processing patterns 2 p areformed in the region P by using a computer (S120). The real processingpatterns 2 p are the processing patterns of the redistributioninterconnects 57 (real patterns 2) used as the above-described leadlines. The end portion of each of the real processing patterns 3 p whichwill become the land electrode 2 a has a circular planar shape and adiameter y1 of 108 μm and a pitch y2 of 180 μm.

Subsequently, as shown in FIG. 8, the real processing patterns 2 p andthe dummy processing patterns 3 p are combined together by using thecomputer (S130). Then, as shown in FIG. 9, the dummy processing patterns3 p (shown by the broken lines in the figure) in the specified space arecalculated from the real processing patterns 2 p by using the computer,and the dummy processing patterns 3 p in the specified space region aredeleted as shown in FIG. 10 (S140). Thereby, the difference in thedensity of the redistribution interconnects 57 configuring the realpatterns 2 and the dummy patterns 3 is reduced as shown in FIG. 2.

A description is subsequently given of the wafer step (S200). As shownin FIG. 11, a substantially circular semiconductor wafer 1W having aplurality of chip regions (A to L) in a shot region ST is prepared(S210). An orientation flat is not shown in the semiconductor wafer 1Win FIG. 11.

In this embodiment, the semiconductor chips 1C are taken out from thechip regions (A to L) of the semiconductor wafer 1W. That is, theredistribution interconnects 47 comprised of the real patterns 2 and thedummy patterns 3 are formed in all the semiconductor chips 1C of thechip regions (A to L).

Subsequently, as shown in FIG. 12, semiconductor elements such as an nchannel type MISFETQ1 and a p channel type MISFETQ2 are formed over themain surface of the semiconductor wafer 1W (to be referred to as“semiconductor substrate 1S” hereinafter) (S220). These MISFETsconfigure, for example, a high-speed SRAM or a logic circuit.

Element isolation regions 21 having an STI (Shallow Trench Isolation)structure are formed over the main surface of the semiconductorsubstrate 1S made of silicon monocrystals; and active regions areseparated from one another by the element isolation regions 21. A p typewell 22 is formed in a region in which the n channel type MISFETQ1 is tobe formed out of the active regions, and an n type well 23 is formed ina region in which the p channel type MISFETQ2 is to be formed. The ptype well 22 is a semiconductor region into which a p type impurity suchas boron (B) has been introduced and the n type well 23 is asemiconductor region into which an n type impurity such as phosphorus(P) or arsenic (As) has been introduced.

The n channel type MISFETQ1 is formed over the p type well 22. Theconfiguration of this n channel type MISFETQ1 is as follows. That is, agate insulating film 24 is formed over the p type well 22 and a gateelectrode 25 a is formed over this gate insulating film 24. The gateinsulating film 24 is, for example, a silicon oxide film and may be ahigh dielectric film having a higher dielectric constant than thesilicon oxide film. The gate electrode 25 a is made of, for example, apolysilicon film into which an n type impurity has been introduced. Thisis carried out to reduce the threshold voltage of the n channel typeMISFETQ1.

A side wall 26 is formed on the both sides of the gate electrode 25 a,and low-concentration n type impurity diffusion regions 27 a are formedin the p type well 22 below the side walls 26. High-concentration n typeimpurity diffusion regions 28 a are formed on the outer sides of thelow-concentration n type impurity diffusion regions 27 a. Thelow-concentration n type impurity diffusion regions 27 a and thehigh-concentration n type impurity diffusion regions 28 a aresemiconductor regions into which an n type impurity has been introducedand the n type impurity is introduced into the high-concentration n typeimpurity diffusion regions 28 a in a higher concentration than thelow-concentration n type impurity diffusion regions 27 a. The sourceregion or the drain region of the n channel type MISFETQ1 is formed bythe low-concentration n type impurity diffusion regions 27 a and thehigh-concentration n type impurity diffusion regions 28 a. A so-calledLDD (Lightly Doped Drain) structure is formed by composing the sourceregion or the drain region from the low-concentration n type impuritydiffusion regions 27 a and the high-concentration n type impuritydiffusion regions 28 a. Therefore, the concentration of an electricfield below the gate electrode 25 a can be eased.

Meanwhile, the p channel type MISFETQ2 is formed over the n type well23. The configuration of this p channel type MISFETQ2 is almost the sameas that of the n channel type MISFETQ1. That is, the gate insulatingfilm 24 is formed over the n type well 23 and a gate electrode 25 b isformed over this gate insulating film 24. The gate electrode 25 b ismade of, for example, a polysilicon film into which a p type impurityhas been introduced. The threshold voltage of the p channel typeMISFETQ2 can be reduced by introducing the p type impurity into the gateelectrode 25 b. In this Embodiment 1, the n type impurity is introducedinto the gate electrode 25 a of the n channel type MISFETQ1 whereas thep type impurity is introduced into the gate electrode 25 b of the pchannel type MISFETQ2. Therefore, it is possible to reduce the thresholdvoltages of both the n channel type MISFETQ1 and the p channel typeMISFETQ2.

A side wall 26 is formed on the both sides of the gate electrode 25 b,and low-concentration p type impurity diffusion regions 27 b are formedin the n type well 23 below the side walls 26. High-concentration p typeimpurity diffusion regions 28 b are formed on the outer sides of thelow-concentration p type impurity diffusion regions 27 b. Thelow-concentration p type impurity diffusion regions 27 b and thehigh-concentration p type impurity diffusion regions 28 b aresemiconductor regions into which a p type impurity has been introducedand the p type impurity is introduced into the high-concentration p typeimpurity diffusion regions 28 b in a higher concentration than thelow-concentration p type impurity diffusion regions 27 b. The sourceregion or the drain region of the p channel type MISFETQ2 is formed bythe low-concentration p type impurity diffusion regions 27 b and thehigh-concentration p type impurity diffusion regions 28 b.

Thus, semiconductor elements such as the n channel type MISFETQ1 and thep channel type MISFETQ2 are formed over the semiconductor substrate 1Sin the semiconductor device in this embodiment.

Subsequently, multi-layer interconnects are formed over thesemiconductor substrate 1S (S230). As shown in FIG. 12, a silicon oxidefilm 29 which is an interlayer insulating film is formed over the nchannel type MISFETQ1 and the p channel type MISFETQ2 overlying thesemiconductor substrate 1S. Plugs 30 reaching the source region and thedrain region of the n channel type MISFETQ1 or the p channel typeMISFETQ2 are formed in the silicon oxide film 29. The plugs 30 are madeof a film stack of a titanium nitride film and a tungsten film which arebarrier metal films.

A silicon oxide film 31 which is an interlayer insulating film is formedover the silicon oxide film 29 having the plugs 30 and first-layerinterconnects 32 are embedded in this silicon oxide film 31. Thefirst-layer interconnects 32 are made of, for example, a tungsten filmand electrically coupled to the plugs 30 formed in the underlying layer.

A silicon oxide film 33 is formed over the first-layer interconnects 32and a plug 34 is embedded in this silicon oxide film 33. The plug 34 isalso made of a film stack of a barrier metal film and a tungsten filmlike the plugs 30. The plug 34 is electrically coupled to thefirst-layer interconnect 32 formed in the underlying layer.

A silicon oxide film 35 which is an interlayer insulating film is formedover the silicon oxide film 33 having the plug 34 and second-layerinterconnects 36 are embedded in this silicon oxide film 35. Thesecond-layer interconnects 36 are made of a film stack of a barriermetal film for preventing the diffusion of copper and a copper (copperor alloy thereof) film.

A silicon nitride film 37 a for preventing the diffusion of copper isformed over the second-layer interconnects 36, and a silicon oxide film37 b is formed over this silicon nitride film 37 a. A film stack of asilicon nitride film 38 a and a silicon oxide film 38 b is formed overthe silicon oxide film 37 b, and a third-layer interconnect 39 isembedded in the silicon nitride film 38 a and the silicon oxide film 38b. This third-layer interconnect 39 is made of a film stack of a barriermetal film for preventing the diffusion of copper and a copper film andelectrically coupled to the second-layer interconnect 36 formed in theunderlying layer.

Like the third-layer interconnect 39, a fourth-layer interconnect 40made of a film stack of a barrier metal film for preventing thediffusion of copper and a copper film is formed over the third-layerinterconnect 39. This fourth-layer interconnect 40 is electricallycoupled to the third-layer interconnect 39 formed in the underlyinglayer. Not shown, a plurality of fuses for saving memories may be formedin the same layer as the fourth-layer interconnect 40 at fixedintervals. The fuses are electrically coupled to a redundancy reliefcircuit so that an address signal for selecting a defective memory cellcan be changed to an address signal corresponding to a redundancy reliefmemory cell by cutting a specific fuse.

A cap insulating film 41 is formed over the semiconductor substrate 1Sto cover the fourth-layer interconnect 40 so as to prevent the diffusionof copper of the fourth-layer interconnect 40 into upper layers, and asilicon oxide film 42 is formed over this cap insulating film 41 by, forexample, plasma CVD (see FIG. 13). The cap insulating film 41 is asilicon nitride film, and the time dependent dielectric breakdown (TDDB)resistance of the cap insulating film 41 and the electromigrationresistance of the fourth-layer interconnect 40 can be improved when aSiCN film is used as the silicon nitride film as compared with a casewhere a SiN film is used.

A plug 43 electrically coupled to the fourth-layer interconnect 40 isformed in the silicon oxide film 42 and the cap insulating film 40. Thisplug 43 can be formed by dry etching the silicon oxide film 42 and thecap insulating film 41 by using a mask (photoresist film), forming aconnection hole reaching the fourth-layer interconnect 40, depositing atitanium (Ti) film, a titanium nitride (TiN) film or a film stackthereof over the silicon oxide film 42 including the inside of theconnection hole as a barrier conductive film, filling a tungsten film inthe connection hole and removing the tungsten film and the barrierconductive film outside the connection hole by CMP or the like.

A fifth-layer interconnect 44 electrically coupled to the plug 43 isformed over the plug 43 above the fourth-layer interconnect 40. Thisfifth-layer interconnect 44 comprises aluminum (Al) as the mainconductive layer and has a structure that the Al film as the mainconductive layer is sandwiched between barrier conductive films which iscomprised of a Ti film and a TiN film. This interconnect can be formedby depositing the lower barrier conductive film, the Al film and theupper barrier conductive film sequentially and dry etching theselaminated films by photolithography using a patterned photoresist filmas a mask.

In this embodiment, the multi-layer interconnects are comprised of thefirst-layer interconnect 32, the second-layer interconnect 36, thethird-layer interconnect 39, the fourth-layer interconnect 40 and thefifth-layer interconnect 44. The multi-layer interconnects serve to forma circuit by electrically coupling a plurality of semiconductorelements.

Subsequently, for example, a thin silicon oxide film 45 and a thinsilicon nitride film 46 are formed as passivation films over thesemiconductor substrate 1S, that is, the silicon oxide film 42 to coverthe multi-layer interconnects (S240). The silicon oxide film 45 and thesilicon nitride film 46 are inorganic insulating films and can be formedby, for example, plasma CVD.

Subsequently, the silicon nitride film 46 and the silicon oxide film 45are dry etched by photolithography using a patterned photoresist film 47as a mask to form an opening portion 48 from which part of thefifth-layer interconnect is exposed. Thereafter, the photoresist film 47is removed by ashing (carbonization).

Subsequently, as shown in FIG. 14, a polyimide resin film 49 which is anorganic insulating film is formed as an insulating film over the siliconnitride film 46 (S250). This polyimide resin film 49 configures asurface protective film (insulating film) for protecting thesemiconductor elements and the multi-layer interconnects of thesemiconductor substrate 1S.

A description is subsequently given of the package step (S300). As shownin FIG. 14, the polyimide resin film 49 is patterned by exposure andashing to remove the polyimide resin film 49 above the opening portion48. Thereby, an opening portion 50 from which part of the fifth-layerinterconnect 44 is exposed is formed in the silicon oxide film 45, thesilicon nitride film 46 and the polyimide resin film 49 over part of thefifth-layer interconnect 44 (S310).

Subsequently, as shown in FIG. 15, after sputter etching is carried outon the surface of the semiconductor substrate 1S, a TiN film and a Tifilm are formed in the opening portion 50 and over the polyimide resinfilm 49 sequentially by sputtering to form a barrier layer 51. A copper(Cu) film is deposited over the barrier layer 51 by sputtering to form aseed layer 52. This seed layer 52 is a seed layer for redistributioninterconnects which will be formed by using the plating process in thesubsequent step.

Subsequently, as shown in FIG. 16, a photoresist film 53 is formed overthe semiconductor substrate 1S by coating and patterned byphotolithography. Thereby, opening portions 54 for formingredistribution interconnects from which part of the seed layer 52 isexposed are formed in the photoresist film 53 overlying part of the seedlayer 52. Out of the opening portions 54, an opening portion 54 a isformed to expose the opening portion 50 formed by removing part of thepolyimide resin film 49 and an opening portion 54 b is formed over thepolyimide resin film 49. The opening portions 54 are used to form theretribution interconnect patterns shown in FIG. 1 and FIG. 2, theopening portion 54 a becomes the real pattern 2 a, and the openingportion 54 b becomes the dummy pattern 3.

Subsequently, when a copper film 55 and a nickel film 56 are depositedsequentially by the electrolytic plating process using the patternedphotoresist film 53 as a mask to form redistribution interconnects 57comprised of the copper film 55 and the nickel film 56, and then thephotoresist film 53 is removed by ashing, the redistributioninterconnects 57 shown in FIG. 17 are obtained (S320). Theredistribution interconnects 57 are formed in such a manner that thereal patterns 2 and the dummy patterns are coexistent within the planeof the semiconductor substrate 1S as shown in FIG. 1 and FIG. 2.

Subsequently, as shown in FIG. 18, by wet etching (cleaning) the seedlayer 52 and the barrier layer 51 using the redistribution interconnects57 as a mask, the seed layer 52 and the barrier layer 51 underlying theredistribution interconnects 57 are left behind and the seed layer 52and the barrier layer 51 excluding these portions are removed.

Subsequently, after the polyimide resin film 58 which is an organicinsulating film is formed as a surface protective film (insulating film)over the semiconductor substrate 15 to cover the redistributioninterconnects 57 (S330) as shown in FIG. 3, the opening portion 59 fromwhich part of the real pattern 2 is exposed is formed in the polyimideresin film 58 over part of the real pattern 2 (land electrode 2 a)comprised of the redistribution interconnect 57 (S340). The openingportion 59 is formed by patterning the polyimide resin film 58 byexposure and ashing and removing the polyimide resin film 58 over theland electrode 2 a of the real pattern 2.

Then, an unshown gold (Au) film is formed over the land electrode 2 a atthe bottom of the opening portion 59 by the electroless plating process.After solder paste is printed on the semiconductor substrate 1S bysolder printing, the solder paste is molten and recrystallized by areflow treatment to form a bump electrode 60 over the above gold film(S350). Pb (lead)-free solder formed from Sn (tin), Ag (silver) and Cumay be used as the solder paste. Alternatively, after a solder ballmolded spherically is supplied into the opening portion 59 instead ofusing the solder paste, the bump electrode 60 can be formed by carryingout a reflow treatment on the semiconductor substrate 1S. The above goldfilm is not diffused into the bump electrode 60 by the reflow treatmentof the solder paste.

Thereafter, the semiconductor substrate 1S in the form of a wafer is cutalong scribe (dicing) regions between the defined chip regions to bedivided into individual semiconductor chips 1C shown in FIG. 1, therebycompleting a semiconductor device in this embodiment. The semiconductorchip 1C in this embodiment can be mounted on a package substrate via thebump electrodes 60. After the semiconductor chip 1C is mounted on thepackage substrate, the bump electrodes 60 are reflowed and an underfillresin is filled into the space between the semiconductor chip 1C and thepackage substrate to manufacture a semiconductor device.

Here, the occupation ratio in the local region in the semiconductorwafer 1W of the redistribution interconnects 57 configuring the realpatterns 2 and dummy patterns 3, for example, the occupation ratio inthe semiconductor chip 1C, and the occupation ratio in the shot regionST is described.

When the occupation ratio of the redistribution interconnects 57 in thesemiconductor chip 1C (shot region ST) becomes low, plating stability,that is, a stable current value cannot be ensured, whereby the thicknessof the plating film (copper film 55/nickel film 56) configuring theredistribution interconnects 57 may become nonuniform within the planeof the semiconductor wafer 1W, or the surface of the center portion ofthe semiconductor wafer 1W may become rough. As already explained withreference to FIG. 4, when the occupation ratio of the redistributioninterconnects 57 is locally nonuniform, a roughened surface is formed atthe end portions of the redistribution interconnects 57 (real patterns2) near the boundary between the peripheral region 90 where the realpatterns 2 are formed (the region where the redistribution interconnects57 are dense) and the central region 80 where the real patterns 2 arenot formed (the region where the redistribution interconnects 57 aresparse).

Meanwhile, when the occupation ratio of the redistribution interconnects57 within the plane of the semiconductor wafer 1W becomes high, thesemiconductor wafer 1W warps due to the relationship with the thicknessof the semiconductor wafer 1W after back grinding. Therefore, the bumpelectrodes 60 cannot be formed after back grinding. Or, thesemiconductor wafer 1W cannot be handled, chipping occurs and the yieldof the post-process drops.

Then, in this embodiment, the dummy patterns 3 are formed in addition tothe real patterns 2 in the redistribution interconnects 57 using the WPPtechnology, and the upper limit and lower limit of the total occupationratio (occupation ratio in the local region) in the shot region ST(semiconductor chip 1C) of the redistribution interconnects 57 comprisedof the real patterns 2 and the dummy patterns 3 are specified tostabilize the step of forming the redistribution interconnects 57 andwork after back grinding and handling, thereby reducing the productionyield of the semiconductor device.

For instance, it is necessary to ensure a plating current value of 6 Aor more for a plating device used in this embodiment to form the platingfilm (the copper film 55 and the nickel film 56 configuring theredistribution interconnects 57) stably. There is correlation betweenthe plating current and the occupation ratio of the redistributioninterconnects 57 within the plane of the semiconductor wafer 1W as shownin FIG. 19. When the plating current is 6 A, it is understood that theoccupation ratio of the copper film 55 is 28.5% in order to form astable plating film of copper (Cu). When the plating current is 6 A, itis understood that the occupation ratio of the nickel film 56 is 33.4%in order to form a stable plating film of nickel (Ni).

Therefore, in this embodiment, the lower limit of the occupation ratioof the redistribution interconnects 57 in the shot region ST(semiconductor chip 1C) including a margin is set to 35% or more.Thereby, the redistribution interconnects 57 can be formed stably andthe production yield can be reduced. A product defect can be suppressedby preventing the end surfaces of the stably formed redistributioninterconnects 57 from being roughened, thereby making it possible toimprove the reliability of the semiconductor device.

When the mass-production of the semiconductor device is taken intoconsideration, it is desired that the warpage of the semiconductor wafer1W having the bump electrodes 60 should be 50 mm or less. It isunderstood from the relationship between the thickness of thesemiconductor wafer 1W having a diameter of 300 mm and the warpage ofthe semiconductor wafer 1W shown in FIG. 20 that when the occupationratio of the redistribution interconnects 57 is 74.3%, as thesemiconductor wafer 1W becomes thinner, the warpage of the semiconductorwafer 1W increases. In this case, the thickness of the semiconductorwafer 1W having a warpage of 50 m or less is 120 μm.

When a reduction in the size of the semiconductor device is taken intoconsideration, it is desired that the thickness of the semiconductorwafer 1W (semiconductor chip 1C) should be smaller, and the lower limitof the thickness of the current product of the semiconductor wafer 1W is100 μm. Therefore, in this embodiment, the upper limit of the occupationratio of the redistribution interconnects 57 in the shot region ST(semiconductor chip 1C) is set to 60% or less from the results obtainedwhen the warpage of the semiconductor wafer 1W is 50 mm or less and thethickness of the semiconductor wafer 1W is 100 μm or less. Thereby, thebump electrodes 60 can be formed stably after back grinding. Thesemiconductor wafer W can be easily handled by suppressing its warpage.Since the chipping and cracking of the semiconductor wafer 1W can beprevented, the production yield of the semiconductor device can bereduced.

Embodiment 2

In the above Embodiment 1, the redistribution interconnects comprised ofthe real patterns which are lines drawn from internal circuits and thefloating dummy patterns are formed in all the chip regions in the shotregion. In this embodiment, redistribution interconnects comprised ofreal patterns and dummy patterns are formed in some of the chip regionsin the shot region. An explanation overlapped with the above embodimentis omitted.

For example, a case where various test chips are arranged in a pluralityof chip regions (A to L) in the shot region ST shown in FIG. 11 will bedescribed. In the shot region ST, test chips requiring the WPPtechnology are formed in certain chip regions (E, F, H) and test chipsrequiring no WPP technology are formed in other chip regions (A, B, C,G, I, J, K, L). That is, semiconductor chips requiring the WPPtechnology and semiconductor chips requiring no WPP technology arecoexistent in the shot region ST.

Since the WPP technology is carried out on the wafer, in thisembodiment, dummy patterns are formed on not only the test chips whichrequire the WPP technology but also the test chips which do not requirethe WPP technology to satisfy the requirement for the occupation ratioof the redistribution interconnects in the shot region as described inthe above Embodiment 1.

FIG. 21 shows the key sections of the chip region E and the chip regionA in the shot region ST in this embodiment. The chip region E shown inFIG. 21 corresponds to the region shown in FIG. 2. That is, thesemiconductor chip 1C shown in the above Embodiment 1 is formed as atest chip in the chip region E in FIG. 21. Therefore, the section of thesemiconductor chip 1C in the chip region E is shown in FIG. 3.

Meanwhile, FIG. 22 is a sectional view of the semiconductor chip in thechip region A. Since the WPP technology is not required, when thesemiconductor chip is formed in the same manner as in the wafer step(S200) shown in FIG. 5, the semiconductor elements (S220), themulti-layer interconnects (S230) including the third-layer interconnect39, the fourth-layer interconnect 40 and the fifth-layer interconnect44, the silicon oxide film 45 and the silicon nitride film 46 (S240)which are organic insulating films, and the polyimide resin film 49(S250) which is an organic insulating film may be formed in thesemiconductor chip in the chip region A. However, in this embodiment,dummy patterns 4 comprised of the redistribution interconnects 57 areformed in the chip region A to satisfy the requirement for theoccupation ratio of the redistribution interconnects in the shot regionST as described in the above Embodiment 1. The dummy patterns 4 can beformed in the same manner as the dummy patterns 3 in the aboveembodiment.

Dummy land electrodes 4 a are also arranged corresponding to the landelectrodes 2 a of the real patterns 2 in the dummy patterns 4. In thisembodiment, as shown in FIG. 22, bump electrodes 60 are formed over thedummy land electrodes 4 a. In the bump electrode forming step (S350), itis desired that almost the same number of bump electrodes 60 as the testchips which require the WPP technology should be formed over the dummypatterns 4 so as to improve work stability (solder wettability).

By forming the dummy patterns 4 in the chip region which does notrequire the WPP technology, the difference in the density of theredistribution interconnects 57 formed by the plating process can bereduced and the occurrence of appearance abnormalities in the realpatterns 2 in the chip region which requires the WPP technology can beprevented.

While the invention made by the inventors has been described in itspreferred embodiments, it is needless to say that the invention is notlimited by the above embodiments and that various changes andmodifications may be made in the invention without departing from thespirit and scope thereof.

For example, while the invention is applied to a semiconductor devicehaving redistribution interconnects in the WPP technology in the aboveembodiments, the invention can be applied to a semiconductor devicecomprising plating interconnects as interconnects for semiconductorelements.

The present invention is effective for a semiconductor device,especially a semiconductor device having redistribution interconnects inthe WPP technology, and is widely used in the manufacturing industry ofsemiconductor devices having a CSP (Chip Size Package) structure inparticular.

1. A semiconductor device comprising: a plurality of multi-layerinterconnects formed over a semiconductor substrate; a passivation filmformed over the semiconductor substrate to cover the multi-layerinterconnects; a plurality of redistribution interconnects formed overthe passivation film; and a first insulating film formed over thepassivation film so as to cover the redistribution interconnects,wherein the plurality of redistribution interconnects have firstpatterns and second patterns which are electrically separated from eachother within the plane of the semiconductor substrate, wherein each ofthe first patterns is electrically coupled to a correspondingmulti-layer interconnect in a first opening portion formed in thepassivation film over a part of the uppermost-level interconnect of thecorresponding multi-layer interconnect, wherein the second patterns areelectrically separated from the multi-layer interconnects, wherein apart of each of the first patterns is exposed in a second openingportion formed in the first insulating film over the part of the firstpattern, and wherein the first patterns and the second patterns arecoexistent within the plane of the semiconductor substrate.
 2. Thesemiconductor device according to claim 1, wherein each of a pluralityof the second patterns has a part that is exposed in a third openingportion formed in the first insulating film over the part of the secondpattern.
 3. The semiconductor device according to claim 2, wherein abump electrode electrically coupled to the part of the second pattern isformed over the part of the second pattern.
 4. The semiconductor deviceaccording to claim 1, wherein a bump electrode electrically coupled tothe part of first pattern is formed over the part of the first pattern.5. The semiconductor device according to claim 1, wherein thesemiconductor substrate configures a semiconductor chip having a firstregion and a second region around the first region within the plane,wherein the first patterns are formed in the second region, and whereinthe second patterns are formed in the first region and the secondregion.
 6. The semiconductor device according to claim 1, wherein arespective planar shape of each of the second patterns is circular orpolygonal with all the corners having a blunt angle.
 7. Thesemiconductor device according to claim 1, wherein the processing sizeof the second patterns is smaller than the processing size of the firstpatterns.
 8. The semiconductor device according to claim 1, wherein theoccupation ratio of the redistribution interconnects within the plane ofthe semiconductor substrate is 35% or more.
 9. The semiconductor deviceaccording to claim 1, wherein the occupation ratio of the redistributioninterconnects within the plane of the semiconductor substrate is 60% orless.